The present invention relates to a mobile communication system and a load distribution method of multiple frequencies in the system, and more particularly, to a CDMA (Code Division Multiple Access) or W-CDMA (Widebanded-CDMA) mobile communication system and a load distribution method of multiple frequencies in the system.
Recently, a CDMA mobile communication system has been widespread because it has such features as large subscriber capacity, asynchronous access capability, strong resistance to mutual interference with other systems, and high concealability.
The conventional CDMA mobile communication system performing frequency assignment will be described referring to FIG. 1.
In FIG. 1, each of base stations: BTS61, BTS62, and BTS63 has three carrier frequency bands of frequencies 71, 72, and 73. Each of these frequencies transmits respectively different pilot signals, and congestions or failures of the frequencies are detected and notified to a radio network controller 11.
Each of mobile units 81 to 83 of CDMA system is able to use the frequencies 71 to 73 as a carrier frequency and has a Pilot search function for different frequencies. Each mobile unit searches the pilot signal in order to detect the base station most appropriate for communication, to thereby notify the radio network controller 11 of a shift regarding the base station when a cell switches.
A present-day frequency assignment method does not focus on frequencies, but determines the frequency on the basis of a Pilot search result of the mobile unit. A carrier terminal using a pilot carrier cell exceptionally performs hard hand-off at times such that the radio network controller 11 designates the frequency. However, even in the case that multiple frequencies cover the same cell as usual, the radio network controller 11 merely examines the frequency selected by the mobile unit whether it is available or not by performing failure checking 37 to failure information 26.
The frequency assignment method in the conventional CDMA mobile communication system as described above has a first problem of inability to distribute loads to each frequency because of not consulting state changes of frequencies when assigning them, and a second problem of inability to consider load distribution in the unit of frequencies due to mobile unit-led frequency assignment.
It is, therefore, an object to provide a mobile communication system capable of distributing loads to multiple frequencies and a load distribution method.